embrogenesis in flowering plants

What key feature distinguishes plant from animal development?

The presence of rigid cell walls, which create physical fate maps and constrain cell movement.

What body plan does the plant embryo already contain?

The adult body plan, including root and shoot apical meristems.

What are the major stages of angiosperm embryogenesis?

Globular → Heart → Torpedo → Mature embryo

What is meant by a “modular, reiterative” body plan?

plants continuously generate new organs via meristems throughout life.

What type of division does the zygote undergo first?

Asymmetric cytokinesis

What two cells are produced by the first zygotic division?

A small apical cell (embryo proper) and a large basal cell (suspensor).

What is the function of the suspensor?

Anchors the embryo and provides positional and nutritional support.

Name three mechanisms that may determine early cell fate.

• Cytoplasmic asymmetry

• Cell size differences

• Positional information

What gene is an early marker of protoderm identity?

ATML1

What is the protoderm?

The outermost embryonic layer that gives rise to the epidermis.

At what stage is the radial axis established?

Octant–Dermatogen stage

What does the cuticle indicate in plant embryos?

Epidermal (protoderm) identity

What evidence supports cell wall involvement in fate determination?

Mutants with altered cytokinesis still form protoderm if the zygote-derived cell wall is intact.

What does Protoderm Model 1 propose?

Radial redistribution of molecules from the suspensor determines fate.

What does Protoderm Model 2 propose?

Cell fate is determined by contact with the zygote-derived cell wall.

What structures define the longitudinal axis?

Apical meristem, cotyledons, hypocotyl, radicle, hypophysis.

What gene is critical for basal axis formation?

MONOPTEROS

What phenotype does the topless mutant show?

Loss of apical structures.

How is the longitudinal axis determined?

Through positional information, hormones, gene regulation, and maternal effects.

What zones exist in the root?

Division zone, elongation zone, differentiation zone.

What is the quiescent centre (QC)?

A group of slowly dividing cells that maintain stem cell identity.

What did laser ablation experiments show?

Older cells can de-differentiate and replace lost initials.

What controls stem cell fate in the root?

Instructive signals from surrounding differentiated tissues

What tissue arises from the E/C initial?

Endodermis and cortex.

What does SHORTROOT (SHR) control?

Endodermis specification

What does SCARECROW (SCR) control?

Asymmetric cytokinesis, not fate.

Where is SHR expressed and where does it act?

Expressed in the stele; moves to and acts in endodermis nuclei.

What happens in shr mutants?

Only cortex forms; no endodermis

What happens in scr mutants?

Mixed cortex/endodermis identity due to failed cytokinesis.

Is cell fate in plants pre-programmed?

No — it is position-dependent and inductive.

How do plants maintain developmental flexibility?

Through meristems and positional signaling.

What does embryogenesis establish?

The axes and body plan of the adult plant.

Which model is best supported by mutant evidence?

Model 2

What mutant supports Model 2?

ts11, rescued by EP3 (a cell-wall–localized protein).